CDC acting director Dr. Jay Bhattacharya delayed publication of a single Morbidity and Mortality Weekly Report (MMWR) paper on COVID-19 vaccine effectiveness, citing concerns about its observational methodology — even though a preliminary summary suggested the 2025–26 formulation cut severe illness risk by about half in adults. The decision, confirmed by HHS spokesperson Andrew Nixon, is being viewed by current and former CDC staff as an atypical level of political appointee intervention in a flagship clinical evidence channel.

The Move

• A CDC study slated for March 19 in MMWR was held after Bhattacharya raised concerns about the “observational method” used to estimate vaccine effectiveness, per HHS.

• The paper used a test-negative design (comparing vaccination status among people testing positive vs. negative for COVID-19), according to current and former CDC employees familiar with the study.

• Current and former CDC officials said it’s rare for a political appointee to stop a single MMWR paper after scientific review and editorial approval.

Why it Matters for Care

• MMWR is a key signal clinicians use for near-real-time guidance; delaying effectiveness data can slow or complicate counseling on seasonal COVID-19 vaccination, especially for higher-risk adults.

• The preliminary summary viewed by NBC News indicated the 2025–26 COVID-19 formulation reduced the likelihood of severe illness by ~50% among adults — a clinically meaningful effect size for shared decision-making.

• If federal messaging becomes less timely or more contested, clinicians may need to rely more heavily on local epidemiology, hospital utilization trends, and non-federal sources when discussing benefits vs. uncertainty.

Between the Lines

• This is happening amid broader Trump administration criticism of longstanding vaccine-effectiveness methods and under HHS Secretary Robert F. Kennedy Jr., whose past anti-vaccine activism has raised concerns among public health experts.

• Test-negative designs are widely used for influenza and COVID-19 VE estimates because they are faster and cheaper than cohort studies and avoid ethical problems of repeating placebo RCTs after licensure.

• The fight is as much about who controls the evidentiary “default” in public health as it is about statistical nuance: slowing publication can create space to question consensus methods and reshape vaccine policy narratives.

What to Watch

• Whether CDC publishes the paper in MMWR after revisions, delays it indefinitely, or the authors submit it to an independent peer-reviewed journal.

• Any formal CDC/HHS methodological guidance tightening or redefining acceptable vaccine-effectiveness designs across federal publications.

• Spillover into ACIP-related policy and litigation: a judge has already put on hold most of Kennedy’s new vaccine advisory committee selections after ruling many were unqualified.

Source: NBC News Health